A delegation of West African leaders has abandoned its trip to Mali to negotiate with the leaders of last week's coup after pro-junta demonstrators staged a sit-in on the airport tarmac in Bamako, the capital.

An official at Ivory Coast's presidency on Thursday said an airplane carrying President Alassane Ouattara, one of a delegation of six heads of state from the Economic Community of West African States (ECOWAS) had returned to the capital Abidjan.

Two diplomatic sources said the other heads of state had also scrapped the planned meeting, designed to pressure army captain Amadou Sanogo to swiftly restore constitutional order after the toppling of President Amadou Toumani Toure.

"Everyone is heading home," one of the diplomats told Reuters, asking not to be named. There was no word on whether the visit would be rescheduled.

However, sources told the AP and AFP news agencies that the regional heavyweights were due to regroup in Abidjan for an emergency meeting after the incident.

Kady Traore, a spokesperson for Ouattara, told Reuters he was "on the plane with the delegation headed to Bamako and it was during the flight that they heard about the protests, and they turned around".

Shortly after Ouattara left Abidjan, scores of pro-junta supporters swarmed the runway at Bamako's airport to prevent the arrival of the team, AFP reported.

Reuters reporters said rival camps of hundreds of youths, some supporting and others opposing the junta, had clashed in central Bamako on Thursday morning, and a group of junta supporters briefly occupied the airport landing strip.

Mali's opposition parties have said they will support a plan devised by the ECOWAS which has called on the leaders of the coup to restore power to the toppled president.

The 15-nation bloc ECOWAS suspended Mali from the organisation during a meeting on Tuesday, following in the footsteps of the African Union as the international community roundly condemned the takeover.

President Toure, 63, was chased out of power just five weeks before the end of his term in office ahead of elections on April 29, by soldiers angry at his handling of a two-month old Tuareg rebellion in the north.

His whereabouts have been unknown since he was overthrown. But he told AFP on Wednesday that he was safe in Bamako and was not being held by the coup leaders.

"I am indeed in Bamako, and thank God my family and I are doing well," Toure said in a brief telephone conversation.

"I am obviously following what is happening, I wish with all my heart that peace and democracy triumph in Mali. I have nothing else to say for the moment."

ECOWAS has said its regional troops are on standby and it has not ruled out the use of force.

Mali meanwhile remains divided over the coup. The majority of the political class has called for a return to constitutional order, but a pro-junta camp has also formed and on Wednesday several thousand marched in favour of Sanogo.

Earlier, the coup leaders had unveiled a new constitution and pledged to hold elections, without specifiying a date.